User blog comment:Parinwaris/The Center Of Theories.../@comment-30134594-20171019130435

Gen 4 Trio (Dialga, Palkia and Giratina)

Remember the Desert Cataconbs before Areda City.

There were many unknown symbols which deciphered a message, but this isnt what im pertaining to. There is a room in the back of the Catacombs containing two pedestrals with the description of needing a "Key of Time" and a "Key of Space".

After reading this, we can speculate that if you get these keys, you can unlock the chance to catch Dialga and Palkia. it's more likely that they sre stationary and appear as they do in Pokemon Platinum in Rifts.

You could possibly get these keys from your parents Post-Game as they are statused as archeologists and they could ask if you can solve what these keys do.

Giratina could be unlocked by having both Dialga and Palkia in your party and a specific item *which i don't know about yet* obtained maybe from Crescent Island or the Eclipse based located in Crescent Island. Possibly, having these in your party unlocks a secret room in the catacombs where if you solve the puzzle, either Giratina appears or a rift to the Disortation world appears.

Add on to this theory if needed. :D